We're told that oxygen causes things to rot, but we're not told anything that would support the claim that it helps preserve footprints. "Oxygen probably helped preserve the footprints of dinosaurs as fossils." - This answer choice discusses both oxygen (mentioned in the second sentence) and footprints (mentioned in the first sentence) however, it suggests that oxygen helps preserve the footprints. Since it's contradicted by the first sentence, it can't be correct. The first sentence tells us that "most fossils" are only partial remains of creatures or imprints they made, which is at odds with this answer choice. "Most fossils involve bodies of creatures that are completely preserved from rotting." - The sentences don't support this answer choice. The second sentence contradicts this statement directly, so this statement can't be the correct answer. "The bark and wood of a petrifying tree preserve the tree’s interior by blocking its exposure to oxygen." - This isn't true at all the second sentence says that during petrification, oxygen cannot get to a tree's bark and wood. Now that we've reviewed these sentences closely, let's look at each of the answer choices and figure out which inference the sentences support. The second sentence is from the section "From Tree to Stone." It is talking about how for petrification to occur, a tree has to be buried so that oxygen cannot get to it, oxygen being the cause of rotting. After all, the sentences can't easily support inferences that are about topics they don't talk about! The first sentence is from the section "A Type of Fossil." It's talking about how most fossils are imprints of ancient creatures or only partial remains of their bodies, such as their skeletons. The next time you see a tree, remember, after a few million years in the right environment, it could turn to stone!īefore we look at the answer choices, let's first consider which topics the given sentences discuss. One national park in the United States, Petrified Forest National Park in Arizona, is famous for its many petrified trees. Petrified wood is found all over the world, and there are even entire forests of petrified trees that you can travel to go see today. Petrified wood can be a rainbow of different colors, with each color corresponding to different elements in the tree’s preserving environment that affect the color of the minerals that form its stone. When the tree’s cells eventually decay, the minerals are left. If mineral-containing water is present, water will go into and out of the tree’s cells and, over time, the minerals in the water will accumulate in the tree’s cells. The environment has to have two more specific characteristics to produce petrified wood: there has to be water in the ground around the tree, and that water has to contain minerals. If oxygen can get to the tree, it will rot instead of turn to stone. The tree has to be buried in such a way that oxygen cannot get to its bark and wood. This has to have happened in a specific environment, though, or petrified wood would not be so rare. In order for a tree to become petrified wood, it must have died and been buried a very long time ago. You can even count the tree rings in some petrified trees and estimate how old the tree grew to be before it was petrified. It’s very cool to see a petrified tree close-up, because it is still precisely life-size you can get an idea of how big the tree was when it was alive, and even see individual tree cells that have been preserved. In contrast, the process of petrification recreates an entire preserved tree in stone. Most fossils are imprints of creatures or partial remains of them, such as their skeletons. Like ancient skeletons of dinosaurs and other organisms preserved in the earth, petrified wood is a type of fossil however, there is a big difference between petrified wood and most fossils. Petrified trees are stone trees, not scared trees! You may have heard the word “petrified” used to describe someone so scared that they have frozen as if turned to stone, but scientists use the word literally to refer to actual stone. Have you ever seen a stone tree? While the idea of a stone tree may sound fantastic, fallen trees can turn to stone in very specific circumstances, producing what scientists call “petrified wood.” “Petra” means stone in ancient Greek, so something “petrified” has been turned to stone.
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